The present invention relates to a diaphragm pump and, more particularly, to a diaphragm pump in which the breakage of the diaphragm, which is caused by over-supply of working fluid due to a negative pressure created through the suction stroke of the diaphragm pump as well as an excessive discharge pressure exerted to the diaphragm, can be prevented.
In the field of diaphragm pumps, it is a commonly known technique to provide an air-discharge valve for outwardly discharging the gas separated by vacuum from the diaphragm-driving working fluid and the gas generated due to cavitation in the working fluid.
However, when such gas is discharged through the air-discharging valve, a small amount of the working fluid is also discharged from the pump. Also, a small quantity of the working fluid leaks through the packing.
In the field of diaphragm pump, therefore, it has been common to provide a cavity in the wall surface of a working fluid chamber filled with working fluid so that the cavity is opposed to the diaphragm, and to install in the cavity a working fluid control valve operative to automatically supply the pump with the working fluid to compensate for the leakage thereof.
The conventionally used working fluid control valve has a columnar valve member resiliently biased toward the diaphragm. The columnar valve member has a side surface provided with a communication port formed therein. The working fluid control valve also has a guide member so disposed in the cavity as to extend toward the diaphragm in the working fluid chamber. The valve member is slidably interconnected with the guide member, having therein a working fluid supply port.
However, in a piping system where more than two diaphragm pumps are connected in parallel, if foreign matters flowing through the piping system adhere to the discharge valve of one diaphragm pump or if a valve member of the discharge valve is scratched or worn, the discharge valve cannot completely be closed. This may result in a possibility that the discharge pressure of another or the other pump is imparted through the incompletely closed discharge valve to the diaphragm of the one of the pumps whereby the diaphragm is strongly urged against a wall surface of the working liquid chamber. Such a phenomenon is liable to occur particularly when the operation of one of double diaphragm pumps or triple diaphragm pumps is stopped while the other pump or pumps are still in operation.
In the working fluid control valve of the conventional diaphragm pump, the surface of the valve member opposed to the diaphragm is more recessed than the peripheral edge of the opening of the cavity. In addition, a gap is formed between the outer periphery of the forward end of the valve member and the inner peripheral surface of the cavity. Thus, when the diaphragm is strongly urged against the wall surface of the working liquid chamber, the diaphragm is liable to be damaged by the nonalignment formed between the forward end face of the valve member and the peripheral edge of the opening of the cavity, or by the gap formed between the inner peripheral surface of the cavity and the outer peripheral surface of the valve member.
The present invention has an object of providing a diaphragm pump in which the working fluid is not excessively supplied due to a negative pressure created through the suction stroke of the pump, and which diaphragm pump is not damaged even when an unduly strong force is exerted thereto, unlike a diaphragm pump provided with the conventional working fluid control valve.
The present invention provides a diaphragm pump which comprises a pumping chamber having a wall formed by a diaphragm reciprocatingly movable to suck and discharge a liquid to be processed into and out of said pumping chamber, a working fluid chamber separated by said diaphragm from said pumping chamber and containing a working fluid for transmitting a pressure change, said working fluid chamber having a wall surface disposed facing said diaphragm, a cavity having an opening formed in said wall surface of said working fluid chamber, diaphragm driving means operative to impart a cyclic pressure fluctuation to the working fluid in said working fluid chamber to thereby reciprocate said diaphragm, a working fluid vessel containing said working fluid, a working fluid supply passage communicating with said working fluid chamber through said cavity, and a working fluid control valve for closing and opening said working fluid supply passage, said working fluid control valve comprising:
a valve member reciprocatingly movable in front of said diaphragm and operative to close the opening of said cavity;
means for biasing said valve member so as to project said valve member out of the opening of said cavity;
working fluid supply passage opening/shutting means for opening said working fluid supply passage when said valve member is positioned close to the opening of said cavity and for closing said working fluid supply passage when said valve member projects from the opening of said cavity; and
means for limiting the maximum distance over which a valve head of said valve member projects from the opening of said cavity.
In one preferred embodiment of the invention, said valve member has a surface disposed facing said diaphragm and so shaped that, when said valve member closes the opening of said cavity, said surface is aligned and continuous with said wall surface of said working fluid chamber.
In another preferred embodiment of the invention, said working fluid control valve has a guide member for guiding the reciprocating movement of said valve member.
In a still another preferred embodiment of the invention, said guide member is a columnar member extending from the bottom of said cavity toward said diaphragm.
In a further embodiment of the invention, the biasing means is disposed between the inner wall surface of said cavity and said valve member.
In a still further embodiment of the invention, said biasing means is disposed between said valve member and said guide member.
In a specific embodiment of the invention, said biasing means comprises a coil spring.